Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$135.44	6.745%	$144.5754	$144.58	$144.60	$144.60
Purchase #2	$51.77	9.142%	$56.5028	$56.50	$56.50	$56.50
Purchase #3	$28.66	4.209%	$29.8663	$29.87	$29.85	$29.90
Purchase #4	$164.60	11.414%	$183.3874	$183.39	$183.40	$183.40
Purchase #5	$170.99	9.123%	$186.5894	$186.59	$186.60	$186.60
Purchase #6	$222.34	12.714%	$250.6083	$250.61	$250.60	$250.60
Purchase #7	$41.78	10.837%	$46.3077	$46.31	$46.30	$46.30
7 purchase totals =	$815.58		$897.8373	$897.85	$897.85	$897.90